Radiocommunication networks were originally developed primarily to provide voice services over circuit-switched networks. The introduction of packet-switched bearers in, for example, the so-called 2.5G and 3G networks enabled network operators to provide data services as well as voice services. Eventually, network architectures will likely evolve toward all Internet Protocol (IP) networks which provide both voice and data services. However, network operators have a substantial investment in existing infrastructures and would, therefore, typically prefer to migrate gradually to all IP network architectures in order to allow them to extract sufficient value from their investment in existing infrastructures. Also to provide the capabilities needed to support next generation radiocommunication applications, while at the same time using legacy infrastructure, network operators could deploy hybrid networks wherein a next generation radiocommunication system is overlaid onto an existing circuit-switched or packet-switched network as a first step in the transition to an all IP-based network. Alternatively, a radiocommunication system can evolve from one generation to the next while still providing backward compatibility for legacy equipment.
One example of such an evolved network is based upon the Universal Mobile Telephone System (UMTS) which is an existing third generation (3G) radiocommunication system that is evolving into High Speed Packet Access (HSPA) technology. Yet another alternative is the introduction of a new air interface technology within the UMTS framework, e.g., the so-called Long Term Evolution (LIE) technology. Target performance goals for LTE systems include, for example, support for 200 active calls per 5 MHz cell and sub 5 ms latency for small IP packets. Each new generation, or partial generation, of mobile communication systems add complexity and abilities to mobile communication systems and this can be expected to continue with either enhancements to proposed systems or completely new systems in the future.
LTE uses orthogonal frequency division multiplexing (OFDM) in the downlink and discrete Fourier transform (DFT)-spread OFDM in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in FIG. 1, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. In the time domain, LTE downlink transmissions are organized into radio frames of 10 ms, each radio frame consisting of ten equally-sized subframes of length Tsubframe=1 ms as shown in FIG. 2.
Furthermore, the resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth. Downlink transmissions are dynamically scheduled, i.e., in each subframe the base station (typically referred to as an eNB in LTE) transmits control information indicating to which terminals and on which resource blocks the data is transmitted during the current downlink subframe. This control signaling is typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe. A downlink system with 3 OFDM symbols as the control region is illustrated in FIG. 3.
LTE uses hybrid-ARQ where, after receiving downlink data in a subframe, the terminal attempts to decode it and reports to the base station whether the decoding was successful (ACK) or not (NAK). In case of an unsuccessful decoding attempt, the base station can retransmit the erroneous data. Uplink control signaling from the terminal to the base station thus consists of: hybrid-ARQ acknowledgements for received downlink data; terminal reports related to the downlink channel conditions, used as assistance for the downlink scheduling (also known as Channel Quality Indicator (CQI)); and scheduling requests, indicating that a mobile terminal needs uplink resources for uplink data transmissions.
If the mobile terminal has not been assigned an uplink resource for data transmission, the L1/L2 control information (channel-status reports, hybrid-ARQ acknowledgments, and scheduling requests) is transmitted in uplink resources (resource blocks) specifically assigned for uplink L1/L2 control information on the Physical Uplink Control Channel (PUCCH). Different PUCCH formats are used for the different information, e.g. PUCCH Format 1a/1b are used for hybrid-ARQ feedback, PUCCH Format 2/2a/2b for reporting of channel conditions, and PUCCH Format 1 for scheduling requests. To transmit data in the uplink the mobile terminal has to be assigned an uplink resource for data transmission, on the Physical Uplink Shared Channel (PUSCH). In contrast to a data assignment in the downlink, in the uplink the assignment must always be consecutive in frequency, in order to retain the signal carrier property of the uplink as illustrated in FIG. 4. In LTE Rel-10 this restriction may however be relaxed enabling non-contiguous uplink transmissions.
The middle single carrier-symbol in each slot is used to transmit a reference symbol. If the mobile terminal has been assigned an uplink resource for data transmission and at the same time instance has control information to transmit, it will transmit the control information together with the data on PUSCH. In Rel-10 also simultaneous transmission of PUSCH and PUCCH in the same subframe is supported.
Uplink power control, i.e., controlling the power at which the mobile terminal is transmitting to the base station, is used both on the PUSCH and on the PUCCH. The purpose is to ensure that the mobile terminal transmits with sufficiently high but not too high power since the latter would increase the interference to other users in the network. In both cases, a parameterized open loop combined with a closed loop mechanism is used. Roughly, the open loop part is used to set a point of operation, around which the closed loop component operates. Different parameters (targets and ‘partial compensation factors’) for user and control plane are used.
Considering uplink power control in more detail, for PUSCH the mobile terminal sets the output power according to:PPUSCHc(i)=min{PMAXc,10 log10(MPUSCHc(i))+PO_PUSCHc(j)+αc·PLc+ΔTFc(i)+ƒc(i)}[dBm],where PMAXc is the maximum transmit power for the carrier, MPUSCHc(i) is the number resource blocks assigned, PO_PUSCHc(j) and αc control the target received power, PLc is the estimated pathloss, ΔTFc(i) is transport format compensator and ƒc(i) is the a UE specific offset or ‘closed loop correction’ (the function ƒc may represent either absolute or accumulative offsets). The index c numbers the component carrier and is only of relevance for Carrier Aggregation. The PUCCH power control has a similar description.
The closed loop power control can be operated in two different modes either accumulated or absolute. Both modes are based on TPC, a command which is part of the downlink control signaling. When absolute power control is used, the closed loop correction function is reset every time a new power control command is received. When accumulated power control is used, the power control command is a delta correction with regard to the previously accumulated closed loop correction. The accumulated power control command is defined as fc(i)=fc(i−1)+δPUSCHc(i−KPUSCH), where, δPUSCHc is the TPC command received in KPUSCH subframe before the current subframe i and ƒc(i−1) is the accumulated power control value. The absolute power control has no memory, i.e. δc(i)=δPUSCHc(i−KPUSCH). The PUCCH power control has in principle the same configurable parameters with the exception that PUCCH only has full pathloss compensation, i.e. does only cover the case of α=1.
In LTE Rel-10, the base station may configure the UE to send power headroom reports associated with the PUSCH periodically or when the change in pathloss exceeds a configurable threshold. The power headroom reports indicate how much transmission power the UE has left for a subframe i, i.e., the difference between the nominal UE maximum transmit power and the estimated required power. The reported value is in the range of 40 to −23 dB, where a negative value shows that the UE did not have enough power to conduct the transmission. The UE power headroom PHc in dB for subframe i is defined as:PHc(i)=PCMAXc−{10 log10(MPUSCHc(i))+PO_PUSCHc(j)+αc(j)·PLc+ΔTFc(i)+ƒc(i)}  (1)
where PCMAXc, MPUSCHc(i), PO_PUSCHc(j), αc(j), PLc, ΔTFc(i) and ƒc(i) is defined above.
It is also possible to enable separate power headroom reports (PHR) for the PUCCH if PUCCH can be simultaneously transmitted with the PUSCH. In such cases either a separate PHR is provided for PUCCH (in dB)PHPUCCHc(i)=PCMAXc−{PO_PUCCHc+PLc+hc(nCQI,nHARQ)+ΔF_PUCCHc(F)+gc(i)},  (2)
or it is combined with PUSCH (in dB),
                                                                        PH                                  PUSCH_and                  ⁢                  _PUCCH                                            ⁡                              (                i                )                                      =                                                            P                                      CMAX                    ,                    c                                                  ⁡                                  (                  i                  )                                            -                              10                ⁢                                  log                  10                                                                               ⁢                  (                                                                                          10                                                                  (                                                                              10                            ⁢                                                                                          log                                10                                                            ⁡                                                              (                                                                  M                                                                                                            PUSCH                                      ·                                                                              c                                        ⁡                                                                                  (                                          i                                          )                                                                                                                                                      ⁢                                                                                                                                                                                                                )                                                                                                              +                                                                                    P                                                              O_PUSCH                                ·                                c                                                                                      ⁡                                                          (                              j                              )                                                                                +                                                                                                                    α                                c                                                            ⁡                                                              (                                j                                )                                                                                      ·                                                          PL                              c                                                                                +                                                                                    Δ                                                              TF                                ·                                c                                                                                      ⁡                                                          (                              i                              )                                                                                +                                                                                    f                              c                                                        ⁡                                                          (                              i                              )                                                                                                      )                                            /                      10                                                        +                                                                                                      10                                                            (                                                                        P                                                      0                            ⁢                            _PUCCH                                                                          +                                                  PL                          c                                                +                                                  h                          ⁡                                                      (                                                                                          n                                CQI                                                            ,                                                              n                                                                  HARQ                                  ,                                                                      n                                    SR                                                                                                                                                        )                                                                          +                                                                              Δ                            P_PUCCH                                                    ⁡                                                      (                            F                            )                                                                          +                                                                              Δ                                                          T                              ×                              D                                                                                ⁡                                                      (                                                          F                              ′                                                        )                                                                          +                                                  g                          ⁡                                                      (                            i                            )                                                                                              )                                        /                    10                                                                                )                                    (        3        )            The parameter definitions associated with these equations are specified above.
The LTE Rel-8 standard has recently been standardized, supporting bandwidths up to 20 MHz. However, in order to meet the upcoming IMT-Advanced requirements, 3GPP has initiated work on LTE-Release 10. One aspect of LTE Rel-10 is to support bandwidths larger than 20 MHz in a manner which assures backward compatibility with LTE Rel-8/9, including spectrum compatibility. This implies that an LTE Rel-10 carrier, which is wider than 20 MHz, should appear as a number of LTE carriers to an LTE Rel-8/9 terminal. Each such carrier can be referred to as a component carrier (CC). Component carriers are also referred to as cells, more specifically primary component carriers are referred to as primary cells or PCell and secondary component carriers are referred to as secondary cells or SCells.
For early LTE Rel-10 deployments, it is expected that there will be a smaller number of LTE Rel-10-capable terminals in operation as compared to many LTE legacy terminals in operation. Therefore, it is desirable to assure an efficient use of a wide carrier also for legacy terminals, i.e., that it is possible to implement carriers where legacy terminals can be scheduled in all parts of the wideband LTE-Advanced carrier. One way to achieve this objective is by means of carrier aggregation (CA). Carrier aggregation implies that, for example, an LTE Rel-10 terminal can receive multiple component carriers, where the component carriers have, or at least have the possibility to have, the same structure as a Rel-8 carrier. An example of carrier aggregation is illustrated in FIG. 5, wherein five 20 MHz component carriers 10 are aggregated to form a single wideband carrier.
The number of aggregated CCs, as well as the bandwidth of the individual CC, may be different for uplink and downlink. A symmetric configuration refers to the case where the number of CCs in downlink and uplink is the same, whereas an asymmetric configuration refers to the case that the number of CCs is different. It is important to note that the number of CCs configured in a cell area may be different from the number of CCs seen or used by a terminal: A terminal may for example support more downlink CCs than uplink CCs, even though the network is configured with the same number of uplink and downlink CCs.
Applying the LTE Rel-8 framework for Power Headroom Reporting to Carrier Aggregation in, e.g., LTE Rel-10, would imply that a PHR for a specific component carrier would be sent on that component carrier itself. Furthermore it is unclear whether a PHR would only be transmitted on a component carrier if the terminal has PUSCH resources granted on that component carrier. In RAN2 it is proposed to extend this framework so that PH for one component carrier can be transmitted on another component carrier. This would enable to report rapid path loss changes on one component carrier as soon as the terminal has PUSCH resources granted on any configured UL component carrier. More specifically, a path loss change by more than dl-PathlassChange dB on any component carrier triggers transmission of a PHR on any (the same or another) component carrier for which the terminal has PUSCH resources granted.
However, these mechanisms for power headroom reporting in systems employing carrier aggregation suffer from certain potential drawbacks. For example, the calculation of PHR is tied to a given PUSCH format. A PHR for a component carrier without PUSCH resources can therefore not be determined due to lack of a valid PUSCH format. The same applies for a PUCCH PHR. Accordingly, it would be desirable to provide methods, systems, devices and software which address these potential deficiencies.